Photoflash lamp

ABSTRACT

A high-voltage type photoflash lamp having an ignition structure including an improved primer material with enhanced breakdown voltage characteristics for the reliable ignition of filamentary combustible material distributed within the oxygen-filled envelope of the lamp. The primer material comprises a particulate fuel such as zirconium powder, a binding agent such as nitrocellulose, and an additive of relatively coarse inert material which is nonconductive and insoluble in the vehicle used in the applied slurry. A preferred additive consists of glass microbeads having a particle size substantially larger than the zirconium powder used.

BACKGROUND OF THE INVENTION

This invention relates to photoflash lamps and, more particularly toflashlamps of the type containing primer material ignited by a highvoltage pulse.

Such flashlamps typically comprise a tubular glass envelope constrictedand tipped off at one end and closed at the other end by a press seal. Apair of lead-in wires pass through the glass press and terminate in anignition structure including a glass bead, one or more glass sleeves, ora glass reservoir of some type. A mass of primer material contained onthe bead, sleeve or reservoir bridges across and contacts the ends ofthe lead-in wires. Also disposed within the lamp envelope is a quantityof filamentary metallic combustible, such as shredded zirconium orhafnium foil, and a combustion supporting gas, such as oxygen, at aninitial fill pressure of several atmospheres.

An improved ignition structure, which provides excellent lampreliability and substantial economies and ease of automated manufacture,is the so-called fritted lead construction described in U.S. Pat. No.4,059,389, of Donald E. Armstrong et al. This is a beadless ignitionstructure comprising a pair of spaced-apart lead-in wires withspherically shaped terminations, a glass frit coating over the lead-inwires, and a coating of primer material over the frit-coatedterminations. The primer may bridge the wire terminations or compriseseparate spaced apart coatings on the respective terminations, with thefilamentary combustible (shredded foil) being in contact with bothterminations to provide a conducting path there between. A primercomposition is described which comprises about 99.0 percent by weight ofzirconium powder and 1.0 percent by weight cellulose nitrate on a driedbasis.

Lamp functioning is initiated by application of a high voltage pulse(e.g., several hundred to several thousand volts, for example, from apiezoelectric crystal in a camera) across the lamp lead-in wires. Thedielectric primer coatings within the lamp then break down electricallyand ignite; the resulting deflagration, in turn, ignites the shreddedcombustible which burns actinically.

Normal lamp-to-lamp variations as well as varying degrees of intimacy ofcontact between primered leads and shredded combustible gives rise to awide range of lamp firing or breakdown voltages. So long as the maximumlamp breakdown voltage is below the output pulse voltage of the camerathe lamps will operate reliably. The maintaining of a suitable controlof the upper limit of lamp breakdown voltage in automated lampproduction has not been a problem.

Prior to use of the present invention, some lamps tended to have verylow breakdown voltages; values as low as 50 volts sometimes beingencountered. Such lamps tended to be undesirably sensitive towardinadvertent ignition by stray electrostatic charges both duringmanufacture and use. Also, there have now appeared on the market camerasthat give voltages to the flash socket at times other than during actualpicture taking. These spurious camera pulses are generally below 100volts but can, however, give rise to inadvertent flashing and lamp lossunder certain conditions when used together with lamps having very lowbreakdown voltages. A minimum breakdown voltage of about 200 istherefore desirable.

In an effort to retain the desirable fritted lead lamp construction, andat the same time elevate the low end of the breakdown voltagedistribution, a number of possible lamp changes have been considered.For example, the application of a thicker frit coating raises theaverage breakdown as well as the maximum values found. Although thepercentages of low voltage lamps is reduced, some lamps remain thatbreak down below 100 volts. Provision of a sufficiently heavy fritcoating to give a minimum breakdown voltage of 200 volts at the sametime gives some lamps of such high voltage that reliability might sufferwith certain camera models.

While it should be theoretically possible to exercise some control ofshred contact with the primer-coated leads and thereby influencebreakdown voltage, in practice this does not appear feasible. The mereshipping and handling of flashlamps causes movement and relocation ofthe mass of shredded combustible.

U.S. Pat. No. 4,059,388 of John W. Shaffer, describes a primer materialcomprising a mixture of combustible metal powder (zirconium), anadditive of one of more metal oxides which are electricallynon-conductive but combustion-supporting, such as WO₃, and a bindingagent, but which is free of oxidizer salts. The metal oxides function asan oxygen donor and do increase the breakdown voltage somewhat. Theelevation of breakdown voltage attainable through such oxide additionalone, however, is insufficient to give lamp populations essentiallyfree of lamps with less than a 200-volt minimum.

A copending application Ser. No. 744,540, Daniel W. Bricker et al, filedNov. 24, 1976 and assigned to the present assignee, describes a primermaterial which includes submicron sized refractory particle additives,such as fumed silica, which are extremely fine compared to the powderedfuel particles (zirconium). This additive does not increase breakdownvoltage significantly but does render the primer more sensitive to lowenergy discharges. Thus its use, while beneficial from the standpoint ofrendering lamp reliability and ignition sensitivity independent of thezirconium powder lot used, actually increased the tendency towardinadvertent electrostatic ignition.

Another U.S. Pat. No. 3,972,673 of Schupp, describes a primer materialwhich comprises a solid mixture of combustible fuel, an oxidizer for thefuel, such as an alkali metal chlorate or perchlorate, and a combustionsupporting oxide of the type which is converted to a lower oxide uponcombustion of the mixture. More particularly, the Schupp patentindicates that certain metal oxide additives in this solid primermixture promote a more complete combustion of the primer fuel. It ishypothesized that the additive is partially reduced through chemicalreaction taking place when the lamp is flashed to provide a source ofoxygen which is readily available for combustion of the primer fuel byreason of the oxygen being generated in the solid mixture. The specificcombustion-supporting oxides indicated as suitable for this applicationcomprise Co₃ O₄, BaCrO₄, Fe₂ O₃, and the higher oxides of nickel. Apreferred primer material composition is given as comprising a solidmixture, in percentages by weight, of 46.1 percent zirconium, 14.5percent sodium chlorate, 31.7 percent Co₃ O₄, and 7.7 percent BaCrO₄ ,and further containing between 1-5 percent of water soluble polymerbinder such as polyvinyl alcohol or polyvinyl pyrrolindone. Thesematerials are dispersed in water to provide a wet paste formanufacturing use.

A later filed, but earlier issued, patent of Schupp, namely, U.S. Pat.No. 3,969,067, describes an improvement over the primer materialdiscussed above in that the composition further includes an alumina geladditive in an amount from about 0.25-2.0 percent by weight of the solidmixture. The patent indicates that this additive modifies the operationof the primer material to promote less sensitivity to prematureaccidental ignition from ambient electrostatic charges without requiringan increase in the maximum energy provided by the firing pulse. Inparticular, the patent indicates that the alumina gel additive can bedispersed in the primer composition with the effect of increasing theaverage breakdown voltage characteristic of the dried primer. A waterslurry of alumina gel would be immiscible in an organic solvent mixturesuitable for use with a nitrocellulose binder. Hence, this approach tothe minimum breakdown voltage problem appears to be somewhat limited asto choice of additive materials and the solvent employed in providing aliquid dispersion for application to ignition structures in lampmanufacturing. Further, the amount of additive employed appears quitecritical. The patent indicates that increased alumina gel concentrationin the primer mixture raises the breakdown voltage level approximately200 volts for each one percent by weight addition of the additive.Accordingly, the production control required to avoid unacceptably highbreakdown voltage levels with fritted lead lamps would appear to besomewhat undesirable for low cost, high speed automated manufacturingprocesses.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of this invention to providean improved photoflash lamp with a reliable ignition means havingenhanced breakdown voltage characteristics.

A particular object of the invention is to provide a primer for highvoltage type photoflash lamps that exhibits a more controlled breakdownvoltage range, with a substantially reduced incidence of lamps havingundesirably low breakdown voltages, while maintaining good flashreliability.

Another object is to provide such a primer in an inexpensive,production-acceptable manner which is applicable to a wide range ofprimer compositions.

These and other objects, advantages and features are attained, inaccordance with the principles of this invention, by the discovery thatan elevation of both the average and low limit of primer breakdownvoltage can be obtained, without diminishing flash reliability, by theaddition of relatively coarse, electrically nonconducting inertparticulate material to the primer composition. Surprisingly, the effectappears rather selective in that the low end of the breakdown voltagerange is influenced more than is the high end of the range. For example,the addition of glass microbeads having an average particle size of 30microns diameter to a primer including powdered zirconium fuel having anaverage particle size of 1.2 microns diameter has, for the first time,made possible the manufacture of the aforementioned fritted lead lampswith the capability of the virtual elimination of lamps with a breakdownvoltage below 200 volts. In general, the additive material may compriseglasses, silica, refractory oxides and other materials which areinsoluble in the vehicle used in providing a liquid dispersion. Hence,there is a broad choice of additive materials suitable for use with awide variety of aqueous or organic solvents.

Preferably, the solid particle size of the additive material is about 10to 50 times larger in diameter than the particle size of the particulatefuel used in the mixture, and the additive is present in an amount fromabout 10 to 60 weight percent of the dried mixture. As discussed above,the principal effect of the additive is to reduce the number of lampswith low breakdown voltage and thereby change the breakdown voltagedistribution for any given population. It is felt that this effectresults from the lengthening of the breakdown path through the primer,such path probably following the interparticle channels formed by thecoarse nonconducting additive.

It is to be noted that the present additive comprises relatively largesolid particles, whereas the previously mentioned alumina gel consistsof porous gel structure of very fine ultimate particle size. Further,the comparatively large proportion of additive employed reduces thecriticality of the amount of additive in the mixture and, thereby,results in an improved primer mixture which is more compatible withautomated production processes than the previously referenced aluminagel additive. The large proportion of additive with a coarse solidparticle size yields an additional benefit which results from thelowered average quantity of combustible metal powder (fuel) used perlamp. Such particle diluted primers results in a freeing of gaseousoxygen for reaction with the shredded combustible in the lamp. Thisbenefit is primarily realized with the safe primers which are free ofoxidizer salts.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be more fully described hereinafter in conjunctionwith the accompanying drawings, in which:

FIG. 1 is an enlarged sectional view of one embodiment of a photoflashlamp in accordance with the invention, wherein primer coatings on thelead-in wires are spaced apart without bridging;

FIG. 2 is an enlarged sectional view of a variation of the lamp of FIG.1, wherein the lead-in wires are bridged with primer; and

FIG. 3 is an enlarged sectional view of another embodiment of aphotoflash lamp in accordance with the invention, wherein one of thelead-in wires has a glass sleeve.

DESCRIPTION OF PREFERRED EMBODIMENT

FIGS. 1 and 2 illustrate fritted lead photoflash lamps of the typedescribed in the aforementioned U.S. Pat. No. 4,059,389, except that theprimer material 16 has a composition in accordance with the presentinvention. Referring to FIG. 1, the high voltage type flashlampillustrated therein comprises an hermetically sealed light-transmittingenvelope 2 of glass tubing having a press 4 defining one end thereof andan exhaust tip 6 defining the other end thereof. Supported by the press4 is an injection means including a pair of metal lead-in wires 8 and 10extending through and sealed into the press in a spaced apartrelationship. The ends of the lead-in wires within the envelope areprovided with smooth and rounded terminations 8a and 10a ofsubstantially spherical shape. The diameter of each terminationpreferably is about 2 to 3 times the diameter of the remainder of thewire. The surface of the lead-in wires and their terminations in theenvelope are coated with an insulating material of glass frit 12. Thefrit glass should have a mean coefficient of thermal expansion whichsubstantially matches that of the glass envelope 2, and preferably, theglass compositions of the frit and the envelope are the same. In thismanner a good glass-to-metal seal is provided in the press area 4, wherethe frit coating 12 typically extends along the leads.

A selected portion 14 on each lead-in wire adjacent to the sphericaltermination thereof may be uncoated with the glass frit insulatingmaterial so as to expose a small area of bare metal wire through coating12. The ignition structure is completed by a coating of primer material16 over the spherical terminations 8a and 10a and portions of theadjacent wire. More specifically, the primer material 16 is disposedover the glass frit coating 12 and must cover any uncoated bare wireportions 14. The respective coatings of primer material 16 on thelead-in wires 8 and 10 are spaced apart from each other. FIG. 2illustrates an alternative approach wherein the primer material 16bridges the terminations of the lead-in wires.

Typically the lamp envelope 2 has an internal diameter of less than onecentimeter and an internal volume of less than one cubic centimeter. Aquantity of filamentary combustible fill material 18, such as shreddedzirconium or hafnium foil, is disposed within the lamp envelope. Theenvelope 2 is also provided with a filling of combustion supporting gassuch as oxygen at a pressure of several atmospheres. Typically, theexterior surface of the glass envelope 2 is also provided with aprotective coating such as cellulose acetate (not shown).

In accordance with the present invention, we have discovered that areliable primer with an enhanced breakdown voltage can be provided bythe use of an additive of relatively coarse inert particulate materialwhich is insoluble and non-conductive and has a particle sizesubstantially larger than that of the combustible powdered fuel. Forexample, primer material 16 may be provided by mixing a particulatefuel, typically a combustible metal powder such as zirconium, with alarger percentage of the inert additive, and a binding agent such asnitrocellulose in a suitable solvent, for example, methyl cellosolve.The resultant primer mixture is then applied, such as by a dip process.For example, after press sealing the lead-in wires into the lamp andprior to filling with shreds and oxygen, the end portions of the fritcoated lead-in wires are dipped into a primer cup which passes throughthe open end of the glass tubing, so as to apply the coating 16 of theprimer material about the wire terminations, as shown in FIGS. 1 and 2.When dried, the primer shows substantially increased ignitionsensitivity for high voltage discharge therethrough.

Alternatively, a thermite-type primer, such as described in U.S. Pat.No. 4,059,388, may be employed. In this instance, the above noted primermixture further includes one or more metal oxides from the group ofmetals comprising cobalt, tungsten, manganese, nickel and/or copper. Theproportion of metal oxides can be from about 1 to 130 percent of thestoichiometric quantity required for chemical reaction with the combinedmetal fuels in the mixture. That is, the amount of metal oxide usedshould fall within plus 30 percent or minus 99 percent of the calculatedstoichiometric quantity required for thermite-type reaction with all themetal powder used. This thermite-type reaction composition increases thebreakdown voltage of the primer as compared to oxidizer free primers soas to preclude inadvertent simultaneous flashing of array lamps due tohigh voltage leakage paths in the interconnecting structure of thecircuitry. The fuel portion of the mixture may also include magnesiumpowder as an additive to lower the electrical breakdown voltage wheresome degree of adjustment to the electrical voltage sensitivity of theprimer is desired. For example, magnesium powder content may be from 0to 30 percent by weight on a dried basis.

Yet a further alternative, although not as desirable, comprises the useof an oxidizer, such as sodium chlorate or potassium chlorate, alongwith the mixture of combustible metal powder, inert additive, andbinder.

Operation of the high voltage flashlamps of FIGS. 1 and 2 is initiatedwhen a high voltage pulse from e.g., a piezoelectric crystal, is appliedacross the two lead-in wires 8 and 10. Electrical breakdown of theprimer causes its deflagration which, in turn, ignites the shreddedmetallic combustible 18. The scraped off portions 14 on the lead-inwires insure reliability of ignition by providing small areas of directcontact between the bare conductor metal and the primer. It has beenobserved, however, that reliable ignition can also be obtained if thescraping step is eliminated and the wires 8 and 10 within the envelopeare left completely coated with frit 12, without providing non-coatedareas 14. It is theorized that such ignition is affected due to thesomewhat porous nature of the upper portions of the frit coating whichare not completely fused, as discussed in the aforementioned U.S. Pat.No. 4,059,389.

In the lamp of FIG. 2, the spark discharge occurs through the primerbridge 16, and the shreds of foil 18 will tend to be supported in theupper portions of the envelope of the bridge. In the lamp above FIG. 1,however, the foil 18 substantially fills the envelope 2 and is incontact with both of the respective primer coatings 16 so as to form anelectrically conducting path therebetween for formation of a sparkdischarge between the lead-in wires and the foil through the respectiveprimer coatings upon application of a high voltage pulse across thelead-in wires. Hence, in high speed automatic production processing, itis not critical whether the primer bridges the leads or not; it is onlynecessary that the foil provides contact between the separate primercoatings.

Referring now to the alternative embodiment of FIG. 3, the high voltagetype flashlamp illustrated therein comprises an hermetically sealedlight-transmitting envelope 22 of glass tubing having a press 24defining one end thereof and an exhaust tip 26 defining the other endthereof. Supported by the press 24 is an ignition means comprising apair of lead-in wires 28 and 30 extending through and sealed to thepress, an insulating sleeve 32 extending within the envelope about thelead-in wire 28, and a mass of primer material 34 bridging the ends ofthe lead-in wires within the envelope. The insulating sleeve 32 may beformed of glass or ceramic and is preferably sealed into the envelopepress 24 at one end so that only the inward end of the sleeve is open.Lead-in wire 30 passes through the press 24 and is formed so that itrests and terminates at or near the opened end of the sleeve 32. Themass of primer material 34, which may be dip applied, is disposed tosubstantially cover the open end of the sleeve 32 and bridge the ends ofthe lead-in wires, as shown in FIG. 3. In accordance with the invention,the composition of primer material 34 includes a finely divided inertadditive material as described hereinbefore with respect to primermaterial 16 in FIGS. 1 and 2.

Typically the lamp envelope 22 has an internal diameter of less than onecentimeter and an internal volume of less than 1 cc. A quantity offilamentary combustible fill material 36, such as shredded zirconium ofhafnium foil, is disposed within the lamp envelope. The envelope 22 isalso provided with a filling of combustion supporting gas, such asoxygen, at a pressure of several atmospheres. Typically, the exteriorsurface of the glass envelope 22 is also provided with a protectivecoating, such as cellulose acetate (not shown).

As described for the lamp of FIG. 1, a wet primer mixture may beprepared and then applied, such as by a dip process, to form theignition mass 34. When dried, the primer shows high ignition sensitivityfor high voltage discharge across the lead-in wires.

Operation of the lamp is initiated when a high voltage pulse, from e.g.,a piezoelectric crystal, is applied across the two lead-in wires 28 and30. Electrical breakdown of the primer causes its deflagration which, inturn, ignites the shredded metallic combustible 36.

By way of specific example, a "control" group of fritted leadconstruction lamps, such as shown in FIG. 1, was primed with thefollowing mixture (shown as weight percentages on a dried basis): 84.14%zirconium powder, 9.95% tungsten trioxide, 0.19% silane adhesionpromoter, 3.93% hydrophobic fumed silica and 1.79% nitrocellulose resin.For application, the material was reduced to a 56% solids slurry withmethyl cellosolve acetate.

A second "test" group of lamps was primed with a test primer made byadding 30% by dried weight of 30 micron diameter glass microbeads to theabove composition. The weight composition of the test primer on a driedbasis was 58.91% zirconium powder, 6.96% tungsten trioxide, 0.13% silaneadhesion promotor, 2.75% hydrophobic fumed silica, 1.25% nitrocelluloseresin, and 30.00% glass microbeads. The lamps of both groups wereflashed with the following results.

    ______________________________________                                        No.         Breakdown Voltage                                                 Primer Lamps    Avg.    Range   % Lamps < 300 Volts                           ______________________________________                                        Control                                                                              30       245     150-2000                                                                              55                                            Test   44       520     200-1400                                                                               5                                            ______________________________________                                    

These data show the elevation in mean lamp firing or breakdown voltagethat results principally from the significant reduction of low breakdownvalues in the voltage distribution obtained. The fraction of lamps thatflash below some given voltage (e.g. 300 volts) is regarded as the mostmeaningful test parameter.

A convenient means of measuring relative flash reliability of differentprimers involves flashing test lamps with a standard 2000-volt piezopulse source and interposing varying degrees of resistance in serieswith the lamps. Lamps with the above control and test primers (withoutand with 30% glass microbeads) were subjected to this test. Forty lampswere used for each group.

    ______________________________________                                        Series Resistance                                                                            Lamps Flashed                                                  ohms           Control       Test                                             ______________________________________                                          680,000      95.0          97.5                                             2,700,000      87.5          95.0                                             6,800,000      85.0          90.0                                             ______________________________________                                    

This test shows, surprisingly, that the addition of 30% by weight ofinert glass microbeads to the primer did not harm lamp reliability and,in fact, appeared to slightly enhance performance. This test functionsby limiting the peak current passed through the lamp after breakdown ofthe primer has occurred. A considerable history of test data supportsthe validity of this test method for predicting relative flashingreliability of different lamp construction and primer formulations.

The principal advantage of this invention is that it provides control ofbrakdown voltage range for high voltage flashlamps of the preferredfritted lead construction, and does so in an inexpensive,production-acceptable way. The resulting beneficiated lamps are lesssubject to inadvertent ignition on certain camera models and during lampproduction itself.

Alternative methods would include the obvious substitution ofparticulate nonconducting material in other than bead shaped particles.While it is felt that microbeads give more predictable void volume andgeometry, and thereby greater freedom from performance idiosyncraciesdue to lot-to-lot variations, this invention is not intended to belimited solely thereto. The composition of the particulate additive mayencompass a variety of materials. Glasses, silica, refractory oxides,and other such materials which are insoluble in the vehicle used, couldbe substituted. The mean particle size is preferably significantlygreater than that of the zirconium (or other combustible metal) powderused. Numerically, the inert particle diameter or mean dimension shouldaverage from 10 to 50 times that of the metal powder. In the examplecited, the glass microbeads were of 30 microns average diameter and thezirconium powder was about 1.2 microns size. The weight percentage ofthe inert nonconducting particulate additive may be from 10 to 60percent on a dried basis. The optimum value is expected to vary with theparticle size and shape chosen; for the glass microspheres cited, theoptimum content is about 30 percent as shown.

Hence, although the invention has been described with respect to aspecific embodiment it will be appreciated that modifications andchanges may be made by those skilled in the art without departing fromthe true spirit and scope of the invention.

What we claim is:
 1. A photoflash lamp comprising:an hermetically sealed, light-transmitting envelope, a quantity of filamentary combustible material located within said envelope; a combustion-supporting gas in said envelope; and ignition means disposed in said envelope in operative relationship with respect to said combustible fill material, said ignition means including a pair of lead-in wires extending into said envelope in a spaced relationship, and a dried coating of primer material covering a portion of at least one of said lead-in wires within said envelope, said coating of primer material having been provided from a mixture comprising a particulate fuel, a binding agent, a solvent and a relatively coarse additive of electrically nonconducting inert particulate material; said additive of inert particulate material being insoluble in said solvent, having a solid particle size which is about 10 to 50 times larger in average diameter than that of said particulate fuel, and being present in an amount from about 10 to 60 weight percent of the dried mixture.
 2. The lamp of claim 1 wherein said combustion-supporting gas in said envelope is oxygen at an initial fill pressure exceeding one atmosphere.
 3. The lamp of claim 1 wherein said fuel is a combustible metal powder.
 4. The lamp of claim 3 wherein said fuel is zirconium powder.
 5. The lamp of claim 1 wherein the inert particulate material of said additive is selected from the group consisting of glasses, silica, and refractory oxides.
 6. The lamp of claim 1 wherein said additive particles are in the form of microbeads.
 7. The lamp of claim 6 wherein said additive comprises glass microbeads.
 8. The lamp of claim 1 wherein the average particle size of said fuel is about 1.2 microns diameter, and the average particle size of said additive of inert particulate material is about 30 microns diameter.
 9. The lamp of claim 8 wherein said additive comprises glass microbeads and is present in an amount of about 30 weight percent of the dried mixture.
 10. The lamp of claim 1 wherein the termination of each of said lead-in wires within said envelope has a smooth and rounded configuration of larger diameter than the remainder of the wire, an insulating material is coated on substantially the full length within the envelope of at least one of said lead-in wires for preventing preignition short circuits through said filamentary combustible material, and said primer material is coated about the smooth and rounded terminations of said lead-in wires, the primer coating on the insulatingly coated lead-in wires being disposed over said coating of insulating material.
 11. The lamp of claim 10 wherein said primer material bridges the terminations of said lead-in wires.
 12. The lamp of claim 10 wherein the respective primer coatings on said lead-in wires are spaced apart from each other, and said filamentary combustible material substantially fills said envelope and is in contact with both of said respective primer coatings so as to form an electrically conducting path therebetween for formation of a spark discharge between said lead-in wires and the combustible material through said respective primer coatings upon application of a high voltage pulse across said lead-in wires.
 13. The lamp of claim 1 further including a sleeve of insulating material extending within said envelope about one of said lead-in wires, said sleeve being sealed to said envelope at one end and open at the other end, the other of said lead-in wires terminating at or near the open end of said sleeve, and said primer material being disposed to substantially cover the open end of said sleeve and bridge the ends of said lead-in wires. 